As a conventional technique for continuing communication using a same IP address even though a terminal moves between networks, there is Mobile IP technology that is defined in RFC3344, for example.
In the mechanism of Mobile IP defined in RFC3344, a FA (Foreign Agent) is placed in a network supporting Mobile IP beforehand. When the terminal (MN: Mobile Node) is connected to the network, the terminal discovers the FA using the protocol of Mobile IP so as to notify FA of address information of the terminal. In addition, the FA reports, to a HA (Home Agent) placed on the Internet, that the terminal is connected, and the HA registers address information on the terminal. A packet transmitted from a communication partner terminal (CN: Correspondent Node) to the terminal is routed to the HA. If a destination address of the packet is one of a terminal registered in the HA, the HA encapsulates the packet to transmit the packet to the FA. The FA transmits the packet extracted from the capsule to the terminal using a layer 2 function in a LAN of the visit destination network. A packet transmitted from the terminal is captured by the FA and is routed to the communication partner terminal.
In addition, a configuration in which the FA is not used can be available (this is called CoA mode). In the CoA mode, when the terminal (MN) is connected to a visit destination network, an address (CoA: Care of Address) in the visit destination network is provided to the terminal by DHCP and the like. In addition, the terminal has a fixed IP address, and the terminal registers the fixed IP address and the CoA to the HA. A packet from a communication partner terminal addressed to the terminal is routed to the HA, and is transmitted to the terminal using the CoA.
[Non-patent document 1] C. E. Perkins, “IP Mobility Support for IPv4,” RFC3344, August, 2002